Several devices and technologies currently exist for transferring characters from a support or carrier sheet to a desired medium. Examples include press-on letters in which individual letters or other characters are formed onto a carrier sheet and then individually removed and transferred to the desired medium. These transfer letters have an adhesive back which permits them to be secured to the medium. A major drawback of this product is the difficulty in properly spacing and aligning the characters on the desired medium. Further, the creation of these characters usually involves a cutting or stamping process. Thus, the edge definition is normally not as good as desired.
Another product currently available contemplates the formation of images of letters or other characters directly onto a transparent, adhesive-backed film. This film is then removed from a carrier layer and secured to the desired medium in its entirety. Although this solves the problem of properly aligning and spacing the characters, the presence of the transparent film on the desired medium is undesirable in many applications.
A further product utilizes a photopolymerizable or cross-linkable film to produce negative images. In this system, selected portions of such film are exposed to various intensities of ultraviolet light. During this exposure, portions which have been exposed to the light source are polymerized or crosslinked by the induction of free radical polymerization. Portions which have not been polymerized or crosslinked are then washed off with an appropriate solvent, leaving behind the desired image of the polymerized material. A major problem with this system is that it requires a threshold of ultraviolet energy before the material will polymerize. Further, it can only be made as a negative system, in which the material forming the image is that which is exposed, unless very exotic chemistry is used.
In another system described in U.S. Pat. No. 4,226,927, a dry transfer element is disclosed which comprises a flexible carrier substrate having a release coating thereon and a photosensitive layer comprising a silver halide emulsion. In this system, the image is first created by exposure to a suitable light source, followed by development of the material with a tanning development agent for the purpose of hardening the gelatin in the emulsion and crosslinking the binder. This permits the nonhardened portion of the material to be removed with an appropriate solvent. In this system, an adhesive material is included in the silver halide emulsion or can be applied as a separate adhesive coating after the photographic layer has been developed and the relief image formed. Although this system overcomes some of the limitations of the other systems described above, it is quite complicated and requires several processing steps.
Accordingly, there is a need in the art for a dry transfer film which is capable of forming images of characters thereon for the purpose of transfer to a desired medium.